1. Field of the Invention
A device, system, and method are disclosed for controlling and/or regulating temperatures of the brain and/or body in a subject.
2. Description of Related Art
Brain injury is common, devastating, and often very expensive to treat. Management of patient temperature by either induction of hypothermia or aggressive treatment of fever has been recommended by the American Heart Association (AHA) as the standard of care for cardiac arrest. Brain temperature management has also been used to treat birth-related cerebral damage and has been FDA approved therapy during cardiac and neurosurgery. Temperature management has been investigated for a variety of central nervous system conditions, including stroke, mechanical brain trauma, and spinal cord injury. A variety of devices have been proposed for therapeutic organ cooling and in particular therapeutic cooling of the brain. Such devices generally fall into one of two broad categories: systemic devices and selective devices.
Systemic devices are widely used today, but selective devices offer compelling advantages. Selective cooling enables the creation of a temperature gradient between the brain and the body core, which can reduce complications associated with body core cooling, resulting in improved patient safety and enabling deep cooling of the brain tissue to achieve neuro-protection.
In general, a high degree of selectivity in temperature management has required a high, and generally undesirable, degree of invasiveness. Surgically invasive devices, such as intravascular devices, often focus on cooling the blood supply to a target area and warming the returning blood supply to prevent cooling of the body core. Intravascular systems and other similarly invasive devices, however, may not be suitable for rapid deployment because they require intervention by a surgeon. A further limitation of catheter-based devices is that they require surgical invasion of a major blood vessel, introducing risk of infection, bleeding, thrombosis, rupture of the blood vessel, dissection of the blood vessel wall and introduction or dislodging debris in the vasculature. These risks are doubled when an intravascular warming catheter is introduced to re-warm blood flow returning from the cooled organ(s).
Other selective, brain focused, non-invasive cooling devices require nebulized fluids that undergo a phase change (evaporation) to maximize a rate of heat transfer from the body. An example of this method is described for example, in U.S. Pat. No. 7,837,722 to Barbut et al. Drawbacks of this approach include exposure of the patient to fluorocarbon coolant (if used as a free flowing liquid), exposure of bystanders to fluorocarbon coolant, and the formation of entrained debris that is difficult to recapture as the coolant leaves the patient. Also, this approach appears to yield a relatively slow cooling rate in human trials, about 2° C. per hour and to our knowledge, a shallow average depth of cooling of <4° C. steady state reduction in brain temperature.
Another selective device is described in U.S. Pat. No. 7,189,253 to Lunderqvist et al. The Lunderqvist devices introduce fluid filled balloons into the nasal cavity and cool the cavity by recirculating cold fluid. These devices control brain temperature by adjusting the temperature of the cooling fluid based on measurement of tympanic membrane temperature. Drawbacks of this approach include a reduction in heat transfer rate due to a reduction in surface area exploited (e.g., the surface area of the sinuses is excluded and the air in the sinuses acts as a barrier to heat transfer) and the heat transfer resistance of the balloon itself. In addition, trauma to the nasal cavity is possible during balloon expansion in the nasal cavity, which is accomplished by restricting fluid flow from the balloon to increase a fluid pressure within the balloon.
These approaches are limited in that they exploit the nasal cavity only, resulting in in a lower heat transfer rate than one which includes, for example, the remainder of the pharynx and the esophagus. For example, the surface area used for heat transfer is greater when the pharynx and esophagus are included. As another example, the heat transfer rate through the perivascular tissue is slow relative to the flow rate of blood rising in the carotid and vertebral arteries. That is to say, the blood flowing in the large arteries of the chest, neck, and head will not thermally equilibrate with the tissue surrounding the arteries during active temperature manipulation, except in circumstances of severely reduced blood flow. The long cold zone of a combined esophageal, pharyngeal, and nasal approach means an enhanced residence time in the cold zone for the blood and thus a greater degree of equilibration and cooling.
Other conventional approaches utilize balloon-based devices, such as those disclosed by Takeda in U.S. Patent Publication Nos. 2008/0086186 and 2009/0177258. Such contained use of fluids generally does not, for example, provide good surface contact with the tissues of the airway or stomach, reducing heat transfer. In addition, such methods can make it difficult to provide access to adjacent areas of the body to promote respiration and/or allow the passage of liquids or gases.
If warming and cooling are used together to create a brain-body temperature gradient, it can be beneficial to use some type of control system to coordinate the warming and cooling activities. Conventional systems for providing temperature controls to separately cool and warm portions of a patient, like that disclosed by Lennox in U.S. Patent Publication No. 2003/0130651, do not have integrated control systems and, as a result, neither temperature control is aware of the action of the other except via measurements of patient temperature. Accordingly, such systems, with their non-integrated controls and reliance on single point measurements of brain and body temperature, respectively, cannot optimally account for time lags between actions in the brain cooling system and responses in body temperature, among other things.